This report describes the typical weather at the Luis Muñoz Marín International Airport (San Juan, Puerto Rico) weather station over the course of an average April. It is based on the historical records from 1992 to 2012. Earlier records are either unavailable or unreliable.
San Juan has a tropical rainforest climate with no dry season. The area within 25 mi of this station is covered by oceans and seas (48%), forests (30%), grasslands (12%), marshes (6%), and croplands (3%).
The month of April is characterized by essentially constant daily high temperatures, with daily highs around 85°F throughout the month, exceeding 89°F or dropping below 81°F only one day in ten.
Over the course of April, the length of the day is essentially constant. The shortest day of the month is April 1 with 12:20 hours of daylight; the longest day is April 30 with 12:48 hours of daylight.
The earliest sunrise is at 5:57am on April 30; the latest sunset is at 6:46pm on April 30; the latest sunrise is at 6:18am on April 1; the earliest sunset is at 6:37pm on April 1.
Daylight savings time (DST) is not observed in 2012.
The median cloud cover is 43% (partly cloudy) and does not vary substantially over the course of the month.
On April 15, a representative day, the sky is clear or mostly clear 45% of the time, partly cloudy 30% of the time, and mostly cloudy or overcast 24% of the time.
The probability that precipitation will be observed at this location varies throughout the month. Precipitation is most likely around April 27, occurring in 59% of days. Precipitation is least likely around April 1, occurring in 55% of days.
Throughout April, the most common forms of precipitation are light rain, heavy rain, moderate rain, and thunderstorms.
Light rain is the most severe precipitation observed during 56% of those days with precipitation. It is most likely around April 3, when it is observed during 33% of all days.
Heavy rain is the most severe precipitation observed during 17% of those days with precipitation. It is most likely around April 24, when it is observed during 11% of all days.
Moderate rain is the most severe precipitation observed during 16% of those days with precipitation. It is most likely around April 7, when it is observed during 9% of all days.
Thunderstorms are the most severe precipitation observed during 11% of those days with precipitation. They are most likely around April 30, when it is observed during 9% of all days.
Either snow is exceptionally unlikely to fall at this location in April or this station does not reliably report precipitation types.
The relative humidity typically ranges from 58% (mildly humid) to 89% (very humid) over the course of a typical April, rarely dropping below 49% (comfortable) and reaching as high as 97% (very humid).
The air is driest around April 1, at which time the relative humidity drops below 64% (mildly humid) three days out of four; it is most humid around April 28, rising above 86% (very humid) three days out of four.
Dew point is often a better measure of how comfortable a person will find the weather than relative humidity because it more directly relates to whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid.
Over the course of a typical April, the dew point typically varies from 66°F (muggy) to 74°F (very muggy) and is rarely below 62°F (mildy humid) or above 76°F (oppressive).
Over the course of April typical wind speeds vary from 0 mph to 17 mph (calm to moderate breeze), rarely exceeding 21 mph (fresh breeze).
The highest average wind speed of 8 mph (gentle breeze) occurs around April 5, at which time the average daily maximum wind speed is 17 mph (moderate breeze).
The lowest average wind speed of 8 mph (gentle breeze) occurs around April 28, at which time the average daily maximum wind speed is 16 mph (moderate breeze).